Gene Behind Rare Eye Disease in Dachshunds Discovered

If applicable to humans, could lead to new treatments, study says

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A specific variation on chromosome 5 was associated with cone-rod dystrophy (CRD) in wire-haired dachshunds, according to a study in the Aug. 8 online issue of Genome Research.

If the mutation is also linked to the condition in humans, and researchers think it might be, this could point the way to new therapies.

"Once you know the gene that's responsible, you can potentially figure out the proteins that are defective and possibly treat these patients," said Dr. Robert Cykiert, an associate professor of ophthalmology at New York University Langone Medical Center in New York City. "Until you know what the defect is, you can't devise any treatment. Once you've at least identified a defective gene, you can work on potential treatments."

"The implications for dogs is that we have the possibility to reduce the frequency of this mutation in the population, and in this way immediately avoid new cases of CRD caused by this mutation," said senior study author Frode Lingaas, a professor at the Norwegian School of Veterinary Science in Oslo. "For humans, the study may help in the identification of the etiology of some cases of CRD, and the dog could also be an extremely valuable model for the development of new treatment schemes for CRD [including gene therapy]."

"In the future, if they could use this model for gene therapy to see whether or not they can replace the gene product with a good protein that actually works in the retina, and they can restore vision in this dachshund, that would be helpful if we were to find same gene defect in humans. That would be good news; we could potentially use gene therapy in humans to restore vision," said Dr. Robert H. Rosa Jr., a professor of surgery at Texas A&M Health Science Center College of Medicine and vice chairman for research in ophthalmology at Scott & White Eye Institute in Temple.

Cone-rod dystrophies are a relatively rare family of eye diseases involving the progressive deterioration of cone function in the retina.

The retina of the eye, which receives visual images then transmits them to the brain, has two main components: rods and cones, Cykiert explained. "The cone cells are basically responsible for your very sharp, central vision. That's what allows you to read and see things far away and also provide you with color vision," he explained. "The rods basically provide you with your peripheral or side vision, and with your nighttime vision. At night, your cones don't work too well. Your rods are what enable you to get around in the dark."

People with CRD develop dayblindness, which can progress to total blindness.

CRD does run in families and, while a few genes have been associated with the condition, others are likely implicated, the authors stated.

One gene mutation had been linked with CRD in miniature long-haired dachshunds, but genes have not yet been implicated in wire-haired dachshunds and pit bull terriers, breeds which also can develop CRD.

Researchers at the Norwegian School of Veterinary Science and the Broad Institute of MIT and Harvard did genome-wide analyses on 13 wire-haired dachshunds with CRD and 13 without the disorder.

A mutation in a portion of the nephronophthisis 4 (NPHP4) gene on chromosome 5 was deleted and appears to be responsible for hereditary CRD in this dog breed. Interestingly, the same gene has been linked with a combination of eye and kidney disease in humans.

The findings could help dogs and, hopefully, one day, humans.

"It may not be the same mechanism in humans, but they think that it is," Cykiert said. "This is going to lead researchers in a direction where they know what to look for."